1. Field of the Invention
The present invention relates to the improvement of a reflecting type photoelectric switching apparatus.
2. Description of the Related Art
As shown in FIG. 5, what is called a coaxial reflecting type photoelectric switching apparatus in which the optical axis of the projected light coincides with the optical axis of the incident light has been conceived by the inventors during the development of the present invention. Light emitting diodes (LEDs) 170A and 170B serving as light projecting devices for emitting the lights having different wavelengths and a photo sensing device 120 for sensing the incident light are fixed to the casing 110. An objective lens 140 is also fixed to the casing 110. The objective lens 140 is constituted by a central portion 144 which functions for the emitted light and an outer peripheral portion 143 which functions for the incident light. A light receiving lens 130 is provided on the side of the photo sensing device 120 of the objective lens 140. A reflecting mirror member 146 is fixed to the surface of the lens 130 on the side of the lens 140. The reflecting mirror member 146 is disposed in such a manner that its reflecting surface 146a is located on the optical axis of the central portion 144 of the objective lens 140. Between the reflecting mirror member 146 and the LED 170B, a projecting lens 180 and a projecting half mirror 160 are respectively fixed to the casing 110.
The light beam emitted from the LED 170B is transmitted through the half mirror 160. The light beam emitted from the LED 170A is reflected by the half mirror 160. Both of these light beams are focused as projected light beams Le onto the reflecting surface 146a of the reflecting mirror member 146 by the projecting lens 180. The projected light beams Le are further reflected by the reflecting surface 146a and collimated by the central portion 144 of the objective lens 140 and projected toward an object to be detected (not shown). A part of the reflected light from the object enters as incident light beams Lr into the outer peripheral portion 143 of the objective lens 140 and is further focused onto the photo sensing device 120 by the light receiving lens 130. A cylindrical separator 150 to separate the projected light beams Le and the incident light beams Lr is provided between the reflecting mirror member 146 and the objective lens 140.
In the foregoing photoelectric switching apparatus, the reflecting mirror member 146 is formed separately from the lenses 130 and 140. Therefore, the reflecting mirror member 146 needs to be fixed to the lens 130 or objective lens 140 with high accuracies with respect to the position and angle. This assembling work is very difficult. In addition, there are such inconveniences that the number of parts increases and the cost of the photoelectric switching apparatus increases.